Occupational studies are conducted to identify and quantify chemical and other causes of cancer and to understand mechanisms of carcinogenesis. Etiologic investigations utilize sophisticated industrial hygiene methods to assess occupational exposures and biochemical components to elucidate mechanisms of carcinogenic action and individual susceptibility. Methodologic studies are designed to improve study techniques and to provide direction for future research. Major etiologic investigations focus on working populations exposed to benzene, other organic solvents, formaldehyde, diesel exhausts, combustion products, electromagnetic fields, pesticides, and silica. Findings linking cancer with occupational exposures included solvents, K-ras mutations and pancreatic cancer; paints and risk of several cancer; sinonasal cancer and exposure to wood dust; mortality among firefighters; solvents and risk of leukemia; bladder cancer and diesel exhausts; inconsistent excesses of lung cancer among silica-exposed workers in China; laryngeal cancer among workers in several dusty occupations in Turkey; benzene and lymphohematopoietic malignancies, agricultural risk factors, t(14;18) translocations and non-Hodgkin's lymphoma, and occupational risk factors for brain cancer. Ongoing projects to evaluate occupational exposures include case-control studies of bladder cancer in Spain and New England, lung cancer in Russia, renal cancer in Eastern Europe, and non-Hodgkin's lymphoma in the U.S. Cohort studies of occupational groups include miners with exposure to diesel exhausts, farmers with exposure to pesticides and other agricultural chemicals, women in many occupations in Shanghai, and cohorts of industrial workers with exposure to benzene, acrylonitrile, formaldehyde, and solvents.